1. Field of the Invention
The present invention relates to a laser machining apparatus having a machining table for fixing a part of a sheet-like workpiece thereon and laser condensing and positioning means, such as an fθ lens, for positioning and condensing a laser beam to the sheet-like workpiece to machine the sheet-like workpiece on the machining table by relatively moving the machining table and the laser condensing and positioning means, and when the machining of the workpiece ends, to move the sheet-like workpiece in the longitudinal direction to repeatedly machine a next machining area thereof.
2. Description of Related Art
FIG. 4 is a perspective view of a main part of a conventional laser machining apparatus for machining a sheet-like workpiece 2 while moving it in the longitudinal direction. The sheet-like workpiece 2 is fixed on the XY table 1 by means of a clamper not shown. The sheet-like workpiece 2 is fed from a supply roll not shown disposed on the right side in the figure and is taken up by a take-up roll not shown disposed on the left side in the figure. Printed boards 3, i.e., perspective merchandise, are disposed on the sheet-like workpiece 2 with a pitch of L2 in the Y direction, i.e., in the longitudinal direction (feed direction), of the sheet-like workpiece 2.
Two fθ lenses 4a and 4b for positioning and condensing a laser beam to the workpiece are disposed above the XY table 1. While the fθ lenses 4a and 4b are disposed so that their X-coordinates coincide each other, their interval L1 is adjustable. The sheet-like workpiece 2 is fixed to the XY table 1 such that the center thereof in the width direction coincides with the center axes O1 and O2 of the fθ lenses 4a and 4b. 
Next, operations of the conventional laser machining apparatus will be explained. Preceding the machining, the interval L1 between the fθ lenses 4a and 4b is adjusted to an integer times of the pitch of the printed board 3 (one time of an equal pitch in the case shown in the figure).
Then, each area defined by the size of the respective fθ lenses 4a and 4b is drilled by the pulsating laser oscillated from a laser oscillator from the side of points A1 and A2 in FIG. 4 for example. When the machining of the area ends, the XY table 1 is moved in the X-direction to machine a next area to be machined. When the machining in the X-direction ends, the XY table 1 is moved in the Y-direction to machine another area to be machined. This operation is repeated until the machining of the whole printed board 3 ends. When the machining of the printed board 3 ends, the sheet-like workpiece 2 is released and is moved in the Y-direction to position a non-finished printed board 3 in correspondence with the fθ lenses 4a and 4b. This operation is repeated until the sheet-like workpiece 2 is totally taken up.
Because the machining is carried out at two spots on the XY table 1, machining efficiency may be improved in case of the laser machining apparatus described above.
By the way, the size (referred to ‘length’ hereinafter) in the Y-direction of the printed board 3 disposed on the sheet-like workpiece 2 may differ. Therefore, when the length of one printed board 3 exceeds a half of a moving stroke of the XY table 1, even if the machining of one printed board 3 may be completed, machining of the other printed board 3 cannot be completed. Thus, not only does it become difficult to position the sheet-like workpiece 2 when moving it, but the machining area must also be calculated again every time the sheet-like workpiece 2 is moved. Therefore, it becomes difficult to control the machining.